Recently, flat-panel displays such as liquid crystal displays and plasma displays have been widely used. However, self-luminous organic EL displays comprising organic EL elements are expected to be the next-generation displays. An organic EL display provides a bright and clear image. Also, the organic EL display provides a wide viewing angle because it is a self-luminous type. In addition, the organic EL display has excellent properties such as rapid response characteristics. Also, the organic EL display has the advantage that the thickness of the display can be easily reduced, because it does not require a backlight. Therefore, the organic EL displays are expected to be widely used in large-screen TVs and the like, in the future.
The organic EL display includes a plurality of organic EL elements and a circuit board that is configured so that the organic EL elements are illuminated. In the circuit board, a thin film transistor (TFT) is connected to each organic EL element in order to control a current flowing through each organic EL element. Also, a correction circuit is connected to each organic EL element in order to suppress a variation in the current flowing through each organic EL element. An insulating layer is formed on the circuit board, and a laminated film having organic EL elements is formed on the insulating layer. In the insulating layer, a connection section is formed to connect the circuit board and each organic EL element.
The organic EL element is disposed on the insulating layer formed on the circuit board. On the insulating layer, positive electrodes and negative electrodes are provided in a matrix shape, and a plurality of organic layers are disposed between the positive electrodes and the negative electrodes. The organic layer includes a light emitting layer containing phosphor molecules, a hole conductive thin layer and an electron conductive thin layer disposed therebetween. When a voltage is applied between the positive electrode and the negative electrode of the organic EL element, holes are injected from the positive electrode into the hole conductive thin layer, and electrons are injected from the negative electrode into the electron conductive thin layer. The holes and electrons are combined in the light emitting layer, whereby light is emitted from the light emitting layer.
The organic EL element is protected by a sealing layer from external air, and is sealed by a sealing glass.
In a process of manufacturing the organic EL display, a process of forming the organic layer greatly influences the display performance. There are several types of methods of forming the organic layer. Among them, an ink-jet method is attracting attention. The ink-jet method applies (prints) a solution, which has an organic material dissolved with a solvent, onto necessary sites, dries the resulting structure, and evaporates the solvent of the solution to form the organic layer. By repeating applying and drying with respect to each organic material, the laminated film of the organic layer can be formed. According to the formation of the organic layer by the ink-jet method, it is easy to form the organic layer over the entire surface of the circuit board and also to make efficiency of the use of material. Therefore, a large-sized display can be relatively easily obtained. Also, the ink-jet method is suitable for manufacturing the display at a low cost.
When the laminated film of the organic layers is formed through the ink-jet method, it is necessary to deposit the organic layers while controlling the thickness of each of the organic layers with an accuracy of a few nm thickness. In the process of forming the organic layers, an ink-jet device is installed in a clean room, and an organic material is applied (printed) under clean environment so that the organic layer is prevented from being contaminated with foreign substances. However, the organic layer may be contaminated with foreign substances such as very fine particles, which are present in a device for applying an organic material or in the internal environment of the clean room. Thus, during the forming of the organic layer, it is difficult to completely prevent the organic layer from being contaminated with foreign substances. Accordingly, the produced organic display may include pixels having defects that are caused by the foreign substances contaminated into the organic layer.
When a voltage is applied between the positive electrode and the negative electrode of the organic EL element having the organic layer contaminated with foreign substances, a current leakage may occur between the electrodes through the foreign substances. Due to this current leakage, the amount of current flowing through the organic layer (light emitting layer) of a pixel including the foreign substances is reduced, and the brightness of the light emitting layer in the entire pixel is reduced. When the amount of current flowing between the electrodes is increased in order to suppress a decrease in brightness, an extra current is required. Also, the power consumption of the organic EL display is increased and the light emission efficiency is degraded. Alternatively, since the amount of leakage current due to foreign substances increases and causes local heating, a degradation of the organic layer may be caused by heat around the foreign substances. In some cases, a large amount of current flows through the foreign substances, no current flows through the organic layer, and the pixel with a foreign substance does not emit light.
A laser repair method has been known as a method of preventing a current leakage caused by foreign substances contaminated into the organic layer. The laser repair method is presented in which a portion of the organic layer which is contaminated with foreign substances or around the portion is irradiated with laser light, thereby a current leakage that may be caused by the foreign substances is prevented. The laser repair method is presented in which a foreign substance or around the foreign substance is irradiated with laser light to insulate the periphery of the foreign substance and a part of the electrode located at the portion contaminated with the foreign substance, thereby a current leakage that may be caused by the foreign substance can be prevented.
For example, Patent Literature 1 describes a method of irradiating an organic layer containing a foreign substance with femtosecond laser light, and thus causing a multi-photon absorption to only a portion having the foreign substance. FIG. 11(a) is a cross-sectional view illustrating the state irradiating foreign substance 10 with femtosecond laser light. FIG. 11(b) is a top view of the state in FIG. 11(a). As illustrated in FIG. 11, a foreign substance is irradiated with a laser light 12 at an adjusted focus of laser light 12. Only a portion around the contaminated foreign substance is insulated by laser light without damaging the periphery of the foreign substance, thereby preventing the occurrence of a leakage current that may be caused by the foreign substance.
Also, Patent Literature 2 describes a method of using a laser to remove an electrode on the periphery of a foreign substance, which surrounds the periphery of the foreign substance, without directly irradiating with laser light an organic layer containing the foreign substance. FIG. 12(a) is a cross-sectional view illustrating the state irradiating with laser light an electrode on the periphery of a foreign substance. FIG. 12(b) is a top view of the state in FIG. 12(a). Negative electrode 5 on periphery of the foreign substance 11 is removed by laser light 12, therefore a foreign substance is not directly irradiated with laser light 12. As a result, the occurrence of a current leakage can be prevented by insulating periphery of the foreign substance 11 without damaging the foreign substance.
Also, Patent Literature 3 discloses a method of irradiating with low-energy laser light a portion of an organic layer around the contaminated foreign substance, without directly irradiating with laser light the foreign substance. FIG. 13 is a top view illustrating a state where the periphery of a foreign substance is irradiated with weak laser light. As illustrated in FIG. 13, when periphery 22 of foreign substance 10 is irradiated with laser light, the energy of the laser light is transmitted from an irradiated region to a defective section. This cycle is repeated several times (four times, irradiation 1 to 4 in FIG. 13) to form high-resistance region 21 around foreign substance 10. No current flows through high-resistance region 21. Thus, a current leakage from a positive electrode to a negative electrode via a foreign substance can be prevented by irradiating with low-energy laser light the periphery of the foreign substance.
What has also been known is a technology to repair a defective pixel by irradiating with laser light a foreign substance, the periphery of the foreign substance, or a transparent electrode (see Patent Literatures 4 to 10).
As described in Patent Literatures 1 to 10, when a foreign substance is contaminated into an organic layer to cause a defect, a foreign substance or the periphery of the foreign substance is irradiated with laser light so as to insulate a laser-irradiated section, thus enabling to prevent a current leakage of a defective section, that is, to repair a defective component. However, Patent Literatures 1 to 3 do not describe a method of adjusting the focal position of the irradiation laser light. If the laser irradiation position is not accurate, a defect is formed by the irradiation of laser light.
For example, in the method described in Patent Literature 1, if the focal position of laser light for irradiating an organic layer is misaligned, the organic layer may be damaged and destroyed. Also, a foreign substance may be finely dispersed by the irradiation of laser light onto a foreign substance, thus causing an increase in leakage current.
Also, in the method described in Patent Literature 2, because the focus of laser light is not properly adjusted, there is a possibility that the focus may be misaligned on the organic layer disposed under the electrode. In this case, an organic layer may be irradiated with laser light, thus causing a degradation of the organic layer. Also, if a sealing layer is formed on the electrode, the sealing layer may be irradiated with laser light, thus degrading the sealing layer and causing a defect in the pixel irradiated with the laser light.
Also, in the method described in the Patent Literature 3, as in the method described in Patent Literature 2, because the focus of laser light is not properly adjusted, a sealing layer or an organic layer formed near an electrode may be irradiated with the laser light, thus damaging the organic layer or the sealing layer and causing a defective pixel.
As a method of adjusting the focal position of laser light, as described in Patent Literature 11, there has been a method of determining the focal position of laser light by forming a process pattern by irradiating with the laser light a process target material while changing the distance between the process target material and a laser head. In Patent Literature 11, line-shaped grooves are formed by irradiating with laser light the process target material while changing the distance between the process target material and the laser head. FIG. 14 illustrates a state where groove 101 is formed on a process target material by irradiating with laser light while changing the distance between the process target material and a laser head. Along a direction of arrow 100, a plurality of groove 101 is formed. As illustrated in FIG. 14, after process patterns (line-shaped grooves 101) are formed at intervals of the distance between the process target material and the laser head, a capacitive sensor attached to the laser head is used to measure a change in capacitance to determine the focal position of laser light.
Also, as a method of adjusting the focal position of laser light, there has been proposed a method of setting the focal position of laser light by measuring the return time of the laser light reflected by a reflective layer of an organic EL equipment (Patent Literature 12).